First tow with Duramax

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Jan 8, 2006
I am going to tow a 7600 lb trailer this weekend
My duramax sits most of the time and has only 12k miles.

Should I go ahead and change the rear differential BEFORE I tow? or after?
The transfer case has new fluids.
Rear and front still has factory fill.
Where I used to work, We had several duramax 3500's that get beat on all day long towing over 12K lbs, being driven on washboard roads, ect... I dont think in thier 200K mile time frame at our company, one of them has ever changed any drivetrain fluid. And hardly ever the engine oil, Untill I started to do it!

12K miles on that diff fluid is fine; Its still brand new. Change it al like 50K miles and your set for life after that, for the most part.
My 09 is very low miles, but tows 13.5k pounds of 5th wheel when it is woken up.

Normal maintenance by OLM here. It tells me when to change engine and trans, then I change everything else by my schedule.

Generally I try to upgrade things like rear end lube so that they are better than stock...
Usually two schools of thought--change it early to remove the break-in wear metals or leave it until the first recommended change by the OEM.

My FX4 has towed nearly half of the miles that it has on it and because I plan to run the wheels off of it, I dumped my factory fill at 13,300 and I am glad that I did. I changed it again at 69,600 and the iron in the oil had reduced by nearly a factor of three (429 versus 148). The $100 question is--would it have hurt to leave the factory fill and dump it at 69,600? Probably not, but the UOA suggests that I did the right thing.
Originally Posted By: Chris142
should have synthetic in the rear diff.its gotta be good stuff considering how long those diffs last.

They ship with a synthetic or blended oil. It has run well past 100k miles in our 3500 service vans with little to no degradation at all.

Note that in our fleet we have never had fluid changes affect the life of a rear end assembly. They are basically a forever piece. Just sold one with a half million miles on it that was quiet as a mouse...
I wouldn't sweat it. 7500 lbs is well within the margin for that vehicle and the fluid is not old. If you tow frequently I'd change it at 30,000.
Originally Posted By: 2010_FX4
Usually two schools of thought--change it early to remove the break-in wear metals or leave it until the first recommended change by the OEM.

I guess I fall in the change out factory fills within the first 5000 mile category. Could not prove it was needed until my 2013 Silverado. The transfer case fluid looked horrible, like some brown sewage, and there were enough metal shavings on the magnetic plug to simulate my cat getting his tail stuck in a light socket. The rear diff was 2 pints low from the factory also. I changed the transfer a second time at 10,000 and the fluid looked great, with very few metal particles on the plug. Probably a fluke occurrence from the factory, but more than ever I am in the change early camp.
ok, I won't sweat it if I can't get it changed before I head out.

I am going to use Mobil 1 75w90 LS.
I have a case of it somewhere in my garage. now only if I can find it. if not it will be castrol syntec.

Transfer case was rebuilt by dealer for noise/vibration since new.

front I will also change, but after the trip.

I had dealership check the rear diffy but we know how dependable they are...
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